SVG support on Windows is added in #3082. Then GTK and themes can use librsvg and so display SVG images. This is probably useful in general. @techee thanks for the pointer.
Just wondering, wouldn't it possibly fix the "win32" theme? The screenshot in #2592 really looks a bit broken but maybe it was because some SVG resource couldn't be read. If it worked, "win32" would be the best solution as it should be closest to user's native windows theme.